Cystic fibrosis (CF) is still an incurable disease affecting 70,000 people worldwide. Lack of new CF therapies is due to poor understanding of disease pathogenesis. Lung complications are responsible for majority of CF mortality. CF airways are characterized by chronic bacterial infections and robust infiltration of leukocytes called neutrophil granulocytes. Neutrophils release their granule cargo and DNA to cause lung damage. Although release of neutrophil-derived inflammatory mediators is of high clinical relevance in CF, its mechanism is unknown. The long-term goal of this project is to determine how neutrophils could be manipulated in CF for preventive and therapeutic purposes. The objective in this particular application is to determine the mechanism and clinical relevance of neutrophil extracellular trap (NET) release in CF. The central hypothesis is that NET formation in CF is mainly triggered by P. aeruginosa flagellar motility, enhanced by the airway inflammatory environment and is associated with clinical measures of lung disease. This hypothesis has been formulated based on strong preliminary data produced in the applicant's laboratory. NETs are composed of a DNA web decorated with histones and granule components. The rationale for the proposed research is that, once the mechanism and clinical importance of Pseudomonas-triggered NET formation will be clear, interfering with it will offer a novel approach to develop innovative new CF therapies. This hypothesis will be tested by pursuing the following specific aims: 1) Establish the clinical relevance of NETs in CF airway disease, 2) dissect the mechanism of P. aeruginosa-triggered NET release, and 3) determine the effect of the CF airway inflammatory environment on NET formation. Based on our preliminary data showing clinical relevance of NETs in CF, in the first aim, correlation studies will be performed between neutrophil markers and measures of CF lung disease severity using CF clinical samples. These data will reveal whether NETs can predict CF lung function decline or are linked to CF pulmonary exacerbations. In the second aim, we will identify the mechanism of P. aeruginosa-stimulated NET formation. In the third aim, we will determine the mechanism how inflammatory molecules present in CF affect NET formation. This research is innovative because it uses novel tools developed by the applicant laboratories to quantitate NETs, it detected several novel NET-related markers in CF clinical samples, it suggests that CF has a significant autoimmune component, and it has the potential to identify new CF biomarker candidates. The proposed research is significant because it focuses on a clinically relevant, unsolved question of CF by using primary human cells and CF clinical samples. In summary, our proposal will deliver essential data to provide a major impact on the field of CF airway inflammation and to be able to design better CF therapies.